Patency of infra-inguinal vein grafts – effect of intraoperative Doppler assessment and a graft surveillance program
Article Outline
Objective
To assess the value of intraoperative graft flow and resistance measurements and a graft surveillance program to predict at-risk infra-inguinal bypass grafts.
Methods
Four hundred sixty-eight infra-inguinal bypass procedures performed between 1995-2006 underwent intraoperative measurement of graft flow and resistance using a Scimed OpDop. These data were correlated with graft outcome at six weeks. Two hundred fifty-four (73%) grafts were entered into a graft surveillance program and the effect of this on primary-assisted graft patency was assessed.
Results
Overall primary and primary-assisted graft patency was 81% and 83% at six weeks and 42% and 64% at three years. Grafts failing by six weeks had significantly lower flow (130.5 mL/min vs. 150.5 mL/min, P = .009) and higher resistance (0.67 peripheral resistance units (PRU) vs. 0.57 PRU, P = .004) than those remaining patent. However, OpDop measured flow and resistance was a poor predictor of graft failure in individual cases (area under ROC curve, 0.57). While there was no statistical difference in primary 18-month patency rates between grafts undergoing surveillance and those undergoing clinical follow up (55% vs. 76%, P = .133), primary-assisted 18-month patency rates were significantly higher in the surveillance group (83% vs. 77%, P = .042).
Conclusion
Intraoperative measurements of graft flow and resistance do not predict graft outcome at six weeks. However, surveillance does identify at-risk grafts and improves mid-term primary-assisted patency.
Autologous vein is the conduit of choice for infra-inguinal bypass grafts.1 Overall, the failure rate of infra-inguinal vein grafts at one year is in the order of 20%-30%, being greater for more distal grafts and for grafts performed for chronic critical limb ischaemia.1 The main causes of early failure (within days to weeks) are technical errors, problems with the graft itself such as poor quality vein, twisting, kinking or external compression, anatomic factors such as poor inflow or poor run-off (ie, poor selection), and systemic factors such as hypercoagulability or sustained periods of systemic hypotension.2, 3 Mid-term failure of vein grafts is primarily due to myo-intimal hyperplasia occurring at the anastamoses or in-graft stenoses, many of which are asymptomatic.4, 5 Late graft failure is primarily the result progression of inflow or distal disease.1 Early identification of a number of these factors may allow the instigation of appropriate treatment resulting in improved graft patency.6
Intraoperative assessment of grafts such as completion angiography,7 angioscopy,8 and intraoperative Duplex9 aim to identify technical problems and detect grafts at ‘high-risk' of early failure. On the whole, these techniques however have not proved particularly effective at reducing early graft failure10, 11 and, although intraoperative Duplex holds the most promise, it is hampered by wide inter-operator variability. We postulated that the SciMed OpDop (SciMed Ltd, Bristol, United Kingdom), a device which standardizes Doppler measured flow and resistance in completed grafts, may be more effective at predicting early graft failure.
Duplex graft surveillance programs have been used in many centers to identify grafts susceptible to mid-term failure by the development of in-graft stenoses or by progression of inflow or outflow disease. Identification of problems allows intervention with the aim of improving graft survival. Despite their widespread use, debate still surrounds their cost and clinical effectiveness.
The aims of this study, therefore, were to first evaluate the effectiveness of intraoperative Doppler graft assessment with the OpDop to predict early graft failure at six weeks, and second to assess the effect of a graft surveillance program on mid-term patency rates.
Methods
Patients
A prospectively gathered comprehensive vascular database of all 468 consecutive infra-inguinal vein graft bypass procedures performed by three consultant vascular surgeons (A.D.H., A.D.F., and T.C.F.S.) between April 1995 and December 2006 was interrogated for demographic, operative, and outcome data. The database recorded demographic details, including mortality data, details of all operative interventions, including amputations, clinical details of all preoperative and postoperative clinic visits, and data on all vascular imaging performed.
Intraoperative graft assessment
Intraoperative assessments of graft function were made following graft completion and restoration of ante-grade flow in all cases. The SciMed OpDop allows an objective assessment of graft function to be made. After calibration for graft size and mean arterial blood pressure, OpDop-calculated graft blood flow and resistance was recorded before and after intra-arterial administration of papaverine hydrochloride (20 mg) to produce peripheral vasodilatation.12 The Doppler probe was attached to the distal portion of the graft, 10-15cm proximal to the distal anastamosis to reduce the error caused by turbulent flow.
Graft flow (mLs/min) and resistance (peripheral resistance units [PRU]) before and after papaverine was correlated with graft outcome at six weeks to assess whether these values could predict early graft outcome.
Surveillance program
The graft surveillance program commenced in 1999 and all infra-inguinal bypass grafts that were clinically patent on hospital discharge after this date were entered into the program and underwent surveillance at six weeks and then again at three, six, nine, 12, and 18 months post-operation. Grafts remaining patent at the end of the surveillance program were followed up clinically, usually on an annual basis. If any intervention was required to maintain graft patency during this period, the surveillance clock was reset and the schedule restarted again six weeks post-intervention. Grafts were assessed by duplex ultrasonography (Philips ATL HDI-3000, Philips Medical Systems, Reigate, United Kingdom) by experienced vascular technicians using either a linear 7 MHz or a curvilinear 3.5 MHz probe. Subjects identified with a significant graft stenosis (three-fold velocity increase, equating to a 70% stenosis13) were discussed with a Consultant vascular surgeon and/or Consultant vascular interventional radiologist and underwent an urgent transfemoral angiogram and balloon angioplasty of the affected segment, usually on the next available list. Stenoses resistant to angioplasty or recurrent stenoses requiring multiple endovascular procedures underwent surgical patch angioplasty.
Subjects undergoing bypass before the commencement of the surveillance program were followed up clinically in the outpatient setting with assessment of pulse status and measurement of ankle: brachial pressure index (ABPI). This follow up usually occurred at six weeks, and at six, 12, and 18 months if no problems were encountered or, more frequently, in cases with tissue loss or postoperative complications. Criteria for performing a graft duplex scan in this group included; development of new symptoms (worsening claudication distance or rest pain); loss of peripheral pulses or graft pulse when previously palpable; or reduction in ABPI >0.15.
Subjects undergoing graft surveillance were compared with the group followed up clinically to assess the effect of surveillance on primary-assisted graft patency.
Statistical analysis
Statistical analysis was performed using SPSS 11.0 (Statistical Package for Social Sciences Inc, Chicago, Ill). Groups were compared at baseline using analysis of variance (ANOVA) test for continuous data and the Chi-squared test for categorical data. In line with published guidelines,14 we defined primary patency as graft patency without a significant stenosis requiring intervention. Primary-assisted patency was defined as graft patency after intervention for a graft stenosis. Intraoperative Doppler measurements were compared using the Mann-Whitney test and the predictive value of these measurements to predict graft outcome were further assessed with receiver operating characteristics (ROC). Kaplan-Meier plots were used to assess patency rates over time, which were estimated by life-table analysis and compared with the log-rank test. A P value of less than .05 was considered statistically significant.
Results
Clinical data
The demographic and operative details of the subjects enrolled are shown in Table I. The mean (standard deviation [sd]) follow-up was 77.5 (101.8) weeks with a shorter length of follow-up seen for fem-distal grafts (52.1 (87.1) weeks, P = .002, ANOVA). Although there was a fairly even split in the numbers of graft type, there were significantly more femoro-above knee popliteal grafts performed than femoro-distal grafts (P = .003, ANOVA). Most grafts were performed for critical limb ischaemia (CLI) (63.3%) and the overwhelming majority used reversed great saphenous vein (GSV) vein as the conduit (84.2%). Subgroup analysis showed that subjects undergoing femoro-distal bypass grafting were significantly older (P = .003, ANOVA) and more likely to be operated on for CLI (P ≤ .001, Chi-squared) than subjects with a femoro-above knee popliteal graft.
Table I. Demographic details of subjects
| All grafts | Fem-AK pop | Fem-BK pop | Fem-distal | P | |
|---|---|---|---|---|---|
| Number | 468 | 176 (38) | 161(34) | 131(28) | |
| Mean age (sd) years | 71.3(10.8) | 69.6(10.8) | 71.1(10.4) | 73.9(11.0) | .003⁎ |
| Gender M:F | 325:143 | 120:56 | 116:45 | 89:42 | .675† |
| Mean follow-up (sd), weeks | 77.5(101.8) | 86.7(105.0) | 88.2(106.2) | 52.1(87.1) | .003⁎ |
| Indication for surgery | |||||
| Disabling IC | 110(24) | 75(43) | 25(16) | 10(8) | <.001† |
| CLI – rest pain | 131(28) | 39(22) | 41(25) | 51(39) | |
| CLI – tissue loss | 165(35) | 57(32) | 46(29) | 62(47) | |
| Popliteal aneurysm | 34(7) | 0 | 33(20) | 1(1) | |
| ALI | 28(6) | 5(3) | 16(10) | 7(5) | |
| Conduit | |||||
| Reversed GSV | 394(84) | 149(85) | 134(83) | 111(85) | .001† |
| In situ GSV | 32(7) | 20(11) | 5(4) | 7(5) | |
| Cephalic vein | 42(9) | 7(4) | 22(14) | 13(10) | |
| Clinical outcome | |||||
| Six-week primary patency | 81% | 85% | 81% | 77% | .142¶ |
| Six-week primary-assisted patency | 83% | 87% | 82% | 77% | .139¶ |
| 18-month primary patency | 53% | 63% | 50% | 43% | <.001¶ |
| 18-month primary-assisted patency | 70% | 78% | 70% | 58% | <.001¶ |
| 30-day mortality | 20(4) | 8(5) | 4(3) | 8(6) | .306† |
| One-year mortality | 61(13) | 19(11) | 12(8) | 30(23) | <.001† |
| Three-year mortality | 87(19) | 26(15) | 22(14) | 39(30) | <.001† |
| Major amputation | 57(12) | 12(7) | 19(12) | 26(20) | .003† |
⁎One way analysis of variance (ANOVA). |
†Chi-squared test. |
¶Log rank test. |
Overall, six-week primary and primary-assisted patency rates were 81% and 83%, respectively, and 18-month primary and primary-assisted patency rates were 53% and 70%, respectively. As expected, more proximal grafts had superior patency rates (Table I).
There was no significant difference in 30-day mortality between the three graft groups, however one-year and three-year mortality rates were significantly higher in subjects undergoing femoro-distal grafts (P = .001, Chi-squared). Significantly more subjects undergoing femoro-distal grafts subsequently required a major amputation (P = .003, Chi-squared) than in the other graft groups. Subjects with grafts failing by six weeks had a poor outcome, with a 33% amputation rate and 12% mortality.
OpDop measurements
Flow and resistance measurements by graft indication and graft type are shown in Table II. There was no significant difference in pre-papaverine graft flow rates or resistance between subjects operated on for non-critical limb ischaemia (intermittent claudication or popliteal aneurysm) or critical limb ischaemia. However, flow and resistance measurements were significantly more favorable for non-critical ischaemia following the administration of papaverine. Graft flow and resistance values, both pre- and post-papaverine, were significantly better in femoro-popliteal grafts compared with femoro-distal grafts (Table II).
Table II. OpDop calculated flow and resistance values by graft indication
| Graft indication | Non-critical limb ischemia | Critical limb ischemia | P |
|---|---|---|---|
| Flow (mLs/min) | |||
| Pre-papaverine | 150.3(70.2) | 139.2(70.2) | .998 |
| Post-papaverine | 260.8(83.4) | 218.1(96.2) | <.001 |
| Resistance (PRU) | |||
| Pre-papaverine | 0.58(0.28) | 0.60(0.27) | .363 |
| Post-papaverine | 0.33(0.21) | 0.37(0.16) | .008 |
| Graft type | Femoro-popliteal | Femoro-distal | P |
|---|---|---|---|
| Flow (mLs/min) | |||
| Pre-papaverine | 155.3(79.7) | 119.5(57.6) | <.001 |
| Post-papaverine | 255.4(101.6) | 186.9(78.4) | <.001 |
| Resistance (PRU) | |||
| Pre-papaverine | 0.54(0.24) | 0.72(0.32) | <.001 |
| Post-papaverine | 0.31(0.13) | 0.45(0.23) | <.001 |
The details of pre- and post-papaverine OpDop measured flow and resistance and the correlation with six-week graft outcome are shown in Table III. Overall, grafts that failed by six weeks had significantly lower flows and higher resistance measurements, both before and after administration of papaverine, than grafts that remained patent. In order to assess whether these measurements could be of use in predicting individual graft failure, receiver operating characteristic (ROC) curves were plotted. The areas under the curves (sd) for pre-papaverine flow and resistance and post-papaverine flow and resistance were 0.568 (0.048), 0.573 (0.048), 0.632 (0.045), and 0.603 (0.045), respectively, indicating that these measurements have a poor discriminating ability to identify the likelihood of an individual graft failing.
Table III. OpDop calculated flow and resistance values for grafts compared to patency status at six weeks
| Graft status at six weeks | Patent | Failed | P |
|---|---|---|---|
| Flow (mLs/min) | |||
| Pre-papaverine | 150.6(82.9) | 130.5(63.9) | .009⁎ |
| Post-papaverine | 243.1(101.2) | 209.1(96.9) | <.001⁎ |
| Resistance (PRU) | |||
| Pre-papaverine | 0.57(0.26) | 0.67(0.35) | .004⁎ |
| Post-papaverine | 0.34(0.15) | 0.40(0.23) | .016⁎ |
⁎Mann Whitney U test; values are mean (standard deviation). |
Graft surveillance
Of the 346 vein grafts that remained patent at six weeks, 254 (73.4%) were entered into a graft surveillance program and the remaining 92 (26.6%) were followed up clinically. Both groups were well matched for baseline demographic and peri-operative details (Table IV). In the surveillance group, 84 (33%) grafts underwent additional therapeutic intervention (percutaneous balloon angioplasty [72], surgical revision [12; patch angioplasty (9), jump graft (3)] after a mean (sd) period of 34.3 (48.2) weeks. All surgical revisions were preceded by an attempt by percutaneous balloon angioplasty. This compares with only four (4%) subjects in the clinical follow-up group undergoing additional intervention (all percutaneous balloon angioplasty) after a mean (sd) of 53.4 (35.4) weeks. There was no statistical difference in primary 18-month patency rates between grafts undergoing surveillance and those undergoing clinical follow up (55% vs. 76%; P = .205, log rank test). However, primary-assisted 18-month patency rates were significantly higher in subjects undergoing duplex surveillance (83% vs. 77%; P = .019, log rank test) (Fig 1). There were a higher proportion of major amputations (amputation of the leg above the level of the ankle) in the clinical follow-up group (12% vs. 4%; P = .005, Chi-squared) and this remained statistically significant when amputations with patent grafts were excluded (7% vs. 2%; P = .013, Chi-squared). All amputations occurred in subjects with either acute or critical limb ischaemia. No subject undergoing bypass surgery for intermittent claudication or popliteal aneurysm underwent a major amputation.
Table IV. Demographic details of subjects in the surveillance and clinical follow-up groups
| Surveillance | Clinical | P | |
|---|---|---|---|
| Number | 254 | 92 | |
| Mean age (sd) years | 70.6(10.3) | 70.6(10.8) | .990⁎ |
| Sex M:F | 181:73 | 68:24 | 0.627† |
| Mean follow-up (sd) weeks | 106.4(93.9) | 89.7(128.8) | 0.189⁎ |
| Indication for surgery | |||
| IC | 73(29) | 20(22) | .155† |
| CLI – rest pain | 70(28) | 24(26) | |
| CLI – tissue loss | 74(29) | 39(42) | |
| Popliteal aneurysm | 26(10) | 5(5) | |
| ALI | 11(4) | 4(4) | |
| Distal anastamosis | |||
| Above knee popliteal | 106(42) | 29(32) | .209† |
| Below knee popliteal | 89(35) | 36(39) | |
| Tibial vessel | 59(23) | 27(29) | |
| Conduit | |||
| Reversed GSV | 205(81) | 85(92) | .057† |
| In situ GSV | 25(10) | 2(2) | |
| Cephalic vein | 24(9) | 5(5) | |
| Primary three-year patency | 52% | 60% | .133¶ |
| Primary-assisted three-year patency | 80% | 70% | .042¶ |
| Major amputation | |||
| All cases | 9(4) | 11(12) | .005† |
| With occluded graft | 5(2) | 6(7) | .013† |
⁎One way ANOVA. |
†Chi-squared test. |
¶Log rank test. |
Fig 1.
Kaplan Meier plots for (a) primary and (b) primary-assisted patency for grafts undergoing duplex surveillance (green) or clinical follow-up (blue).
Fig 1a. Numbers at risk (events)
Months 0 3 6 9 12 5 18 Clinical 92 (9) 67 (15) 53 (16) 48 (16) 54 (17) 37 (17) 34 Duplex 254 (30) 220 (62) 180 (85) 153 (96) 136 (102) 118 (108) 109 Fig 1b. Numbers at risk (events)
Months 0 3 6 9 12 15 18 Clinical 92 (9) 67 (15) 53 (15) 49 (15) 55 (16) 38 (16) 35 Duplex 254 (13) 237 (31) 208 (35) 197 (39) 187 (42) 178 (42) 164
Discussion
The 18-month patency rates reported in this series (53% primary and 70% primary-assisted) appear slightly lower than reported in other series. There are a number of explanations for this. The patency rates reported are pooled data for all types of graft performed and for all indications and degree of urgency. The primary patency rates may appear low due to the high use of duplex surveillance in this study and the strict criteria used for graft failure (>70% stenosis). Other series with clinical follow-up will inevitably report higher primary patency rates (as was seen in the clinical follow-up group of our study). Another major factor may be our department's strict policy on using vein as a conduit whenever possible. In a recent audit, only 3% of our infra-inguinal grafts used a prosthetic conduit (1.6% as a composite). Our aggressive policy of using vein as a conduit will undoubtedly mean that some conduits are poorer quality than others and will lead to a reduction in overall patency rates for the group as a whole. We firmly believe that this approach is the correct one, given the significantly poorer outcome observed with prosthetic grafts.
Quality control assessment, therefore, following completion of venous bypass grafts, is an important component of infra-inguinal bypass surgery, being able to detect technical errors that, if left uncorrected, may result in early graft failure. Even in the absence of technical errors, quality control assessment has the potential to identify grafts deemed to be at ‘high-risk' that may benefit from aggressive postoperative medical management such as formal anticoagulation, the use of Dextrans, or entry into a high-intensity surveillance program.
A number of quality control methods have been assessed, including completion angiography,7 intraoperative duplex scanning,15 angioscopy,11 and Doppler flow assessment.16
Completion angiography has been considered the gold standard in graft quality control assessment as it gives good visualisation of the graft, anastamoses, and run-off vessels and helps to exclude technical errors with the anastamoses and the graft.7 Despite this, angiography only offers a 2D image, and up to 25% of grafts with a normal completion angiogram have haemodynamic abnormalities detected by an early duplex scan.17 Furthermore, completion angiography has not been shown to alter short- or intermediate-term graft patency.10
Angioscopy had its proponents in the 1990s8 and proved more useful in assessing the quality of the venous conduit than angiography but has fallen out of favor, largely due to the inability to adequately assess the distal vasculature.11
Intraoperative Duplex assessment of grafts appears to be the most useful modality to assess graft function and may have the ability to predict future stenotic development and graft failure.9, 18, 19 Duplex assessment, however, is user dependent and subject to wide interoperator variability and thus there may be advantages to using a device capable of standardizing measurements graft flow and resistance, such as the OpDop. A number of studies have assessed completion Doppler spectral analysis of graft flow and resistance, but these have generated conflicting results. Beard et al were one of the first to assess this and found that, although graft flow was of little value in predicting graft outcome, high post-papaverine peripheral resistance correlated well with one-month patency.12 While these findings have been confirmed in several later studies,9, 20 there is further conflicting data published demonstrating no relationship between resistance values and early graft outcome.16, 21
In this present study, which contains a significantly larger number of cases than previous studies, we identified a significant relationship between low graft flow and high graft resistance with early (six-week) graft failure. Despite this correlation, our ROC analysis failed to identify cut-off flow or resistance values useful to predict a graft that has a high risk of short-term failure. We therefore found that, for individual cases, the Doppler flow measurements were unable to predict the short-term outcome of grafts. The identification of a simple test to predict the outcome of bypass grafts would be extremely welcome and would allow focused surveillance of those grafts most at risk. This study, however, provides further evidence that while intraoperative graft flow and resistance measurements have an association with graft outcome, no single measure has sufficient ability to risk stratify individual grafts. The reasons for this disappointing finding are likely to be complex and multi-factorial. Either these measurements are unable to identify grafts that are not technically satisfactory or technically sound grafts undergo early failure secondary to other factors in the post-operative period (for example, systemic hypotension, coagulopathy, or external compression). As a result, we have discontinued the use of the OpDop as a quality control assessment in our unit.
This study also assessed the value of duplex surveillance on mid-term patency of venous bypass grafts. While this is not a randomized controlled trial, there were no significant changes to operative and clinical practice over the study period, and, as a result, the two follow-up groups are comparable. In this present study of 468 vein grafts with an average follow-up of 18 months, we have demonstrated a significant benefit to vein graft surveillance compared to clinical follow-up both in terms of graft patency (80% vs. 70%; P = .042) and amputation rates (4% vs. 12%; P = .005).
Vein graft surveillance has been a topic that has been the subject of much debate over the years and a number of randomized trials have provided conflicting views on the benefit of graft surveillance programs. Lundell et al22 assessed the value of duplex surveillance versus clinical follow-up in 106 vein grafts in a randomized controlled trial and found superior patency rates in grafts followed up by duplex assessment (primary assisted patency 78% vs 53%; P ≤ .05). No significant benefit, however, was found in terms of limb salvage rates. A further randomized controlled trial, Ihlberg et al,23 failed to show any beneficial effect of duplex scanning on graft patency or limb salvage in a surveillance program of 185 vein grafts. This study, however, has been criticized for having numerous radiologists performing the surveillance duplex scans (n = 22, of which 39% were trainees) and for only obtaining 60% follow-up in the duplex arm. In a follow-up study by the same authors, subjects who adhered to trial protocol (90 subjects clinical follow-up, 57 subjects duplex surveillance) were analyzed, and no difference in graft patency rates was found, despite a higher graft revision rate in the duplex group.24
The largest and most recent randomized study to date is that by Davies et al25 and was designed to settle the matter. This trial identified no benefit to duplex surveillance over clinical surveillance in terms of patency rates or limb salvage rates. They also concluded that there were no differences in health-related quality of life and that the costs of a duplex surveillance program were greater than clinical surveillance. This randomized clinical trial (RCT) had originally planned to recruit 1200 subjects but, due to difficulty in recruitment, only 594 subjects were recruited from 29 centers in the UK and Europe. This equates to an average of 20 subjects per center, with 10 randomized to duplex surveillance. The small number of patients per center means that the trial could be subject to variations in the results of treatments in the different centers – for example, some centers may have a high complication rate from graft angioplasty and skew the patency rates of the surveillance group. Thus, while multicenter randomized controlled trials may offer the best evidence for guiding generalized practice, an equivocal finding does not mean that duplex surveillance cannot be successful in individual centers with a well run program and a low complication rate from intervention.
Conclusion
This present study has demonstrated no significant advantage of intraoperative Doppler wave analysis of completed infra-inguinal vein grafts on short term graft patency. We have, however, demonstrated that, in our hands, a well conducted vein graft surveillance program results in superior mid-term graft patency rates, translating into improved limb salvage rates.
Author contributions
References
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Competition of interest: none.
PII: S0741-5214(09)00229-8
doi:10.1016/j.jvs.2009.02.002
© 2009 Society for Vascular Surgery. Published by Elsevier Inc. All rights reserved.
